rec.autos.simulators

I don't doubt that the gravitational acceleration of 9.81 m/s2 is
right but somehow it often looks too low for me.

I saw a rally race on TV yesterday and I recognized that if the cars
jump big jumps they are on the ground again after about 1 sec :)
That means even with high velocities they have contact again after a
very short period of time.

When I try to reproduce this with a "9.81-sim" like my car simulator
or Carmageddon 2 (the only game I've installed) it is as if you're
flying like a
bird for several seconds.
It looks as if the gravity "attacks" to late after jumping.

I think in games where jumping is not very common this is not a
problem, but if you're making a stunt game (like me) this seems quite
unrealistic.
Just to have a look I took 20m/s2 of gravity and in many situations it
seems much more realistic.

I was wondering which other physical fact influences the gravitational
motion of the car body, but if it was only the real-world's air
friction, the cars in my sim would fall even slower since I don't have
air friction implented yet.

Did you notice that behaviour?
Thanks!

Robert

Which way is that high velocity? It's along their direction of travel - not
vertically.  The vertical velocity imparted by a small jump is not a lot.

i.e if something is moving up at 9.81 m/s - it'll take 2 seconds to arrive
back at the point it started (1 seconds to slow down to 0 - 1 seconds to
accelerate back to the same point again)

9.81m/s is infact 35km/h.  The verticle element of the velocity of a car is
no where NEAR that much - while it's horez. element may be in excess of
200km/h

Doug

The cars are heavy, and travel upto about 120mph.  They can't go too far.
Remember that they use suspension to absorb the jumps, so it requires a much
better ramp for them to take off.

I expect it's a case of your simulated cars having less advanced suspension
and as such going much higher.  Obviously it'll take longer to fall from a
greater height ;-)

The rate at which you jump/land is completely seperate to the speed you are
travelling along the road at.  Split your thoughts into components.  You
take off with a velocity of x m/s in the upwards direction caused by the
reaction with the ground.  This is reduced at a rate of about 9.81m/s2 until
you land.  I suspect you are using rather large ramps to take off with (you
mention a stunt simulator), and have little suspension modelling to absorb
the effect of the ramp.

If a ramp 1 metre long produces a vertical component of reaction with the
tyre of 100N, then the tyre will accelerate upwards with the velocity of x
m/s.  The suspension takes this velocity and absorbs it into the car's mass
which means overall, the car has sustained 100N of upwards force.  This
model should work until you run out of capacity for stored energy, or it is
released before you take off.

Having read that back to myself it makes no sense, and I can't think of
another way to express it.  Can anyone else help?  Anyone cope with a
translation?

Andy
--
PC-Based Multimedia System
http://www.andylaurence.pwp.blueyonder.co.uk/pcbmms

The weight of the car has nothing to do with the height it will jump and
fall.

i.e a 100 kg weight projected up at 9.81 ms will take 2 seconds to fall back
to earth. The same is true of a 1g lead shot. (ignoring air resistance)

Doug

        Dave

x1 = x0+v0*t + 1/2at^2
v0 = 0
x0 = 2
x1 = 0
t = Sqrt+(  4 / a )
a = -9.81
t = 0.6 sec

without any aerodynamics load.

in Formula One Family on AbMotors they said that with actual wings on F1
at 200kmh the car could drive on a ceiling. Obviously WRC wings are much
smaller than that ;o)

So maybe t final could something like 0.45sec wich is small !!! usualy WRC
do 1 meter high jumps.
=> t ~= 0.3 sec

Try to fall an object from 1 or 2 meter in your sim a time it with your
watch.

regards,
--
Sebastien TIXIER - Game Developer
Dynamics and Car Physics
http://www.eden-studios.fr
GPLRank Normal:-44.24 Monster:-124.44

That is indeed true, but a 100N force will send a 1Kg radio controlled model
a lot further into the air than a 1000Kg rally car, and as such it will take
longer to come back down.

Andy (not making himself very clear)
--
PC-Based Multimedia System
http://www.andylaurence.pwp.blueyonder.co.uk/pcbmms

were not talking of the same thing. your talking about the initial impulse that
cause
the jump and we're arguing about the time to touch back the ground ;o)

Yeah (I assume you mean negating air resistance).

Yeah, but the time taken to get back to the ground is proportional to the
height of the jump.  This in turn is proportional to the impulse.  I was
just trying to say that the vehicle could be going higher in his simulation,
yet seem a similar height because of camera angles.  I'm not disagreeing
with anyone on this thread (so far), just adding a different perspective.
Sorry for the confusion.

Andy
--
PC-Based Multimedia System
http://www.andylaurence.pwp.blueyonder.co.uk/pcbmms

Jesse

;-) ;-) ;-)

Great analogy for those strict "in a vacuum neglecting all friction" people.

Jesse

Ignoring dampers, it probably involves the static
deflection but you can't really ignore dampers.

Jonny

  I noticed it in my sim too :0)  It didn't seem like gravity was working
correctly, but sure enough, dropping the car from a set height caused it to
take xx seconds to hit the ground, just like it should...  It looks different
than on tv though, I agree :0)  

 For a stunt type game, you might want to play with gravity to get it however
"feels" best, and is most fun...  You might check to see how high your cars are
being launched off the ramps, they might be beyond current world records :0)

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

People 'complained' about that in my sim as well. Weird. Tested it,
and it's ok.

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

I'm testing gravities of 1,5*g to 2*g now, and my colleague also says
it looks much better now (he's a graphics artist ;))

A problem that arises with the higher gravity is that things like
loopings are harder to manage, so I think I should find some
compromise.

Robert